Group Service in CORBA Xing Gang Supervisor: Prof. Michael R. Lyu Marker: Prof. Irwin K. C. King, Prof. John C. S. Lui 5/3/2019

Outline Motivation Background OmniORB Proposed System Schedule Group Service Group-based System Group Communication in CORBA CORBA FT Service OmniORB Proposed System Schedule 5/3/2019

Motivation Goal Use Group Service to Manage the Redundant Entity Provide Fault Tolerance via Entity Redundancy Use Group Service to Manage the Redundant Entity Group Service: Provide Reliable Group Communication (multicast) CORBA FT Service Specification 5/3/2019

Idea of Group Communication Group Communication is to gather a set of processes or objects into a logical group, and to provide primitives for sending messages to all group members at the same time with various ordering guarantees A group constitutes a logical addressing facility since messages can be issued to groups without having to know the number, identity, or location of individual members. Groups have proven to be very useful for providing high availability through replication: a set of replicas constitutes a group, viewed by clients as a single entity in the system. 5/3/2019

Total Order Multicast 5/3/2019 Total order multicast is one of the most useful primitives for group communication. Simply stated, it ensures that messages sent to a group are delivered in the same order to all members of the group. Total ordering of messages is required for instance in replication, to ensure that the replicated data is kept consistent. Figure 1.2 shows two messages sent by two clients to a set of servers with and without total ordering. A total order protocol may need to delay the actual delivery of a message to the application for ensuring correct ordering. 5/3/2019

Active Replication 5/3/2019

Primary-Backup Replication 5/3/2019

Group-Base System Isis Horus Ensemble (Maestro): Cornell Univ. Totem: UCSB Transis: Hebrew Univ. Phoenix: Swiss FIT 5/3/2019

Different Approaches Integration Approach : integrates an existing group communication system within an ORB Interception Approach : intercepts messages issued by an ORB and maps them to a group communication toolkit Service Approach : provides group communication as a CORBA service beside the ORB 5/3/2019

Integration Approach 5/3/2019

Orbix+Isis Orbix Client Isis Server1 Server2 Server3 5/3/2019

Interception Approach 5/3/2019

Eternal 5/3/2019

Service Approach 5/3/2019

OGS 5/3/2019

Approaches Comparison Integration Interception Service Transparency + Ease of Use Portability Interoperability Modularity CORBA Compliance Performance Simplicity 5/3/2019

CORBA FT Service(1) Time Line Objective Wide range of fault tolerance RFP Issued -- April 1998 Initial Proposals Submitted -- October 1998 Joint Revised Submission -- October 1999 Approved by OMG – December 1999 Objective Wide range of fault tolerance Simple low-cost clients Highly reliable servers Passive and Active replication Both automatic and application-controlled fault tolerance mechanisms Strong replica consistency, when needed 5/3/2019

CORBA FT Service(2) Fault Tolerance Properties Replication Styles Infrastructure-Controlled and Application-Controlled Object Group References and Alternative Destinations At-Most-Once Invocation Fault Detection and Notification Checkpointing and Logging 5/3/2019

Architectural Overview 5/3/2019

omniORB omniORB is a robust, high-performance CORBA 2 ORB, developed by AT&T Labs research omniORB is freely available under GPL Feathers C++ binding Native IIOP Multithread Naming and Lifecycle Service omniORB3 5/3/2019

Add Group Service to omniORB Objective Robustness Completeness Performance 5/3/2019

ORB Multicasting Enhance POA to provide group management interface to ORB Multicast Algorithms (protocol) Isis/Hours/Ensemble Totem Transis Semiotics at least once at most once exactly once 5/3/2019

Assumptions No Low Level Group Communication Toolkit NO IP Multicast No Network Partition Problem Higher Level Group Management Service Use CORBA FT Service Interface 5/3/2019

Active Replication Requirement Group Management (AT&T) Multicast Implementation Fault Tolerance Service Spec. Compliance 5/3/2019

Experimentation & Evaluation Application Active Replicate Name Server Evaluation of Current Specification Discovery Overhead Reliability 5/3/2019

Schedule Multicast Protocol August 31,2000 Integrate with AT&T Group Management Service November 30,2000 Applications & Evaluation March 31,2000 5/3/2019

Q&A 5/3/2019

Thank You!! 5/3/2019